Gloom Beasties are the troublemakers of CastleVille. Unlike normal enemies in games such as this, their real weapon is that they suspend any actions that you may try to initiate in a radius around them. It is difficult to predict when Gloom Beasties will appear - this happens depending on actions that you have performed previously.
Note that the number of Gloom Beasts in your kingdom at any one time is limited. This limit increases depending on your level.
A clever tactic for dealing with Gloom Beasts is to encourage them into a small and safe part of your kingdom, where you do not perform many actions. If you keep them there and reach the maximum limit for Beasts, then no new ones will appear in more important areas of your kingdom.
Below is a brief guide to the Gloom Beasts, including what actions trigger their spawning - this will allow you to perform the trick above more easily:
The Gloom Rat is summoned by harvesting a Farm. You can also produce it with a potion costing 5 Reputation Points. It has 3 Health, and rewards you with a Gloom Rat Tail, Bone and between 1 and 2 Energy when you defeat it.
This appears when you tend to an animal or chop trees. Its potion costs 8 Reputation and the Wolf has 5 Health Points. It gives you Gloom Wolf Hair and Bone when you defeat it, as well as between 2 and 3 Energy.
When you tax a house, normally above 600 Coins, a Gloom Thief may appear. To use its potion requires 10 Reputation Points. It has 8 Health Points. It gives you the Thief's Cloak, and 2-3 Energy on defeat.
The Gloom Goblin can only be summoned with a Potion costing 12 Reputation Points. It has 9 Health before it can be defeated - at which point you will receive a Gloom Goblin Ear, and 2-3 Energy.
Follow this guide to summon Beasts and keep them in an unimportant corner of your kingdom. Purchase a Super Clobber from the Market using Reputation Points to make it far easier to deal with Beasties - this will save you Energy and generally make everything much easier.